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Fish kill

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Dead fishes pile up on the western shores of Salton Sea, California

Fish kill is an event in which dead or dying fish are observed in a body of water. Fish kill can represent small numbers of fish or hundreds of thousands of fish. Different causes can lead to fish kill.[1] The most common cause is reduced oxygen in the water, which in turn may be due to factors such as drought, algae bloom, overpopulation, or a sustained increase in water temperature. Infectious diseases and parasites can also lead to fish kill. Toxicity is a real but far less common cause of fish kill.[2] It is very difficult to predict when a fish kill is going to come about. Even when conditions that contribute to fish kill are known to exist, prevention is hard because often conditions cannot be improved and fish cannot be safely removed in time. In small ponds, mechanical aeration and/or removal of decaying matter (such as fallen leaves or dead algae) may be reasonable and effective preventive measures.

Fish kills are often the first visible signs of ecological hypoxia and are usually investigated as a matter of urgency by environmental agencies to determine the cause of the hypoxic event and whether or not the cause was man made, due to pollution, or naturally occurring. If it is a dissolved oxygen-related fish kill, large fish seem to be affected first. If it is a cold-related fish kill, juvenile fish and/or species that are not cold-tolerant may be selectively affected. If toxicity is the cause, species are more generally affected and the event may include amphibians and shellfish as well.

Oxygen Depletion

Warm water fish generally need dissolved oxygen (DO) concentration of at least 5 ppm (5 mg/l). Fish can endure short periods of reduced oxygen. However, fish might not recover from DO levels below 2 mg/l and begin to die when they fall below 1 mg/l. Depleted oxygen levels are the most common cause of fish kills. Oxygen levels normally fluctuate even over the course of a day and are affected by weather, temperature, the amount of sunlight available, and the amount of living and dead plant and animal matter in the water.[3]

Oxygen enters the water through diffusion. Algae and aquatic plants also produce oxygen through photosynthesis. The amount of oxygen that can be dissolved in water depends on the atmospheric pressure, the water temperature and whether the water is salty.[4] For example, at 20°C (68°F) and one atmosphere of pressure, a maximum of 8 mg/l of oxygen can dissolve in sea water (35 mg/l salinity) while a maximum of 9 mg/l of oxygen can dissolve in fresh water. The amount of oxygen that can be dissolved in the water decreases by about 1 mg/l for each 10°C increase in water temperature above 20°C.

Oxygen depletion can result from a change in any of several factors or unfavorable combination of factors.

Drought

A drought can lead to lower water volumes so that even if the water contains a high level of dissolved oxygen, the reduced volume may not be enough for the fish population. Droughts often occur in conjunction with high temperatures so that the oxygen carrying capacity of the water may also be reduced.

Turnover

Another cause of fish kills is pond turnover, sometimes called inversion or pond rollover.[5] Turnover results in low dissolved oxygen levels and can lead to fish kill. It is usually only a serious problem in ponds 4 feet deep or deeper. During the late spring and summer, the pond water develops stratified layers as colder water sinks to the bottom. (Even though cooler water has more oxygen carrying capacity, this water in the bottom layer of the pond is not exposed to the plant or atmospheric sources of oxygen and so may have as little as 1 mg/l of dissolved oxygen.) Turnover occurs when the top layer of warm, oxygenated water mixes with the lower layer. A sudden cooling of the top layer of water causes the mixing. This sudden cooling may be caused by heavy rains, which in areas such as the Southeastern United States may be an every afternoon occurrence, a rapid temperature drop, a heavy cloud cover which affects the amount of sunlight, or a strong, steady wind blowing in one direction for a long period of time.

In some coastal areas, another type of turnover occurs in ponds or lagoons that have a direct connection to saltwater. Some of these connections are at too high an elevation for there to be regular tidal influence. On extreme spring tides, the ponds are flooded with saltwater, which is denser and therefore heavier than the freshwater of the pond. When the saltwater enters, it sinks to the bottom, displacing the bottom water that has a low dissolved oxygen level.

Algae bloom

An algae bloom is the appearance of a large amount of algae or scum floating on the surface of a body of water. Algae blooms are a natural occurrence in nutrient-rich lakes and rivers, though sometimes increased nutrient levels leading to algae blooms are due to fertilizer or animal waste runoff. A few species of algae produce toxins, but most fish kills due to algae bloom are a result of decreased oxygen levels. When the algae die, decomposition uses oxygen in the water that would be available to fish. A fish kill in a lake in Estonia in 2002 was attributed to a combination of algae bloom and high temperatures.[6] When people manage algae blooms in ponds, it is recommended that treatments be staggered to avoid too much algae dying at once, which may result in a large drop in oxygen content.

Biological decay

Just as an algae bloom can lead to oxygen depletion, introduction of a large amount of decaying biological material in general to a body of water leads to oxygen depletion as microorganisms use up available oxygen in the process of breaking down organic matter. For example, a 10-mile-long fish kill in September, 2010, in the Sangamon River in Illinois was traced to discharge of animal waste into the river from a large dairy operation. The illegal discharge resulted in a complete kill of fish, frogs, mussels and mudpuppies.[7]

Water temperature

A fish kill can occur with rapid fluctuations in temperature or sustained high temperatures. Generally, cooler water has the potential to hold more oxygen, so a period of sustained high temperatures can lead to decreased dissolved oxygen in a body of water. An August, 2010, fish kill in Delaware Bay was attributed to low oxygen as a result of high temperatures.[8]

A massive (hundreds of thousands) fish kill at the mouth of the Mississippi River in Louisiana, September, 2010, was attributed to a combination of high temperatures and low tide. Such kills are known to happen in this region in late summer and early fall, but this one was unusually large.[9]

A short period of hot weather can increase temperatures in the surface layer of water, as the warmer water tends to stay near the surface and be further heated by the air. In this case, the top warmer layer may have more oxygen than the lower, cooler layers because it has constant access to atmospheric oxygen. If a heavy wind or cold rain then occurs (usually during the autumn but sometimes in summer), the layers can mix. If the volume of low oxygen water is much greater than the volume in the warm surface layer, this mixing can reduce oxygen levels throughout the water column and lead to fish fill.

Overstocking

Fish kill due to insufficient oxygen is really a matter of too much demand and too little supply for whatever reason(s). Overstocking of fish (or an unusually large spawn) can thus lead to fish kill by itself. Recommended stocking densities are available from many sources for bodies of water ranging from a home aquarium or backyard pond to commercial aquaculture facilities.

Cold temperatures

Fish kills can result from a dramatic or prolonged drop in air (and thus, water) temperature. This kind of fish kill is selective - usually the dead fish are species that cannot tolerate cold. This has been observed in cases where a fish native to a more tropical region has been introduced to cooler waters, such as the introduction of the Tilapia to bodies of water in Florida. Native to Africa’s Nile River, the tilapia stop feeding when water temperatures drop below 60°F and die when it reaches 45°F. Thus, tilapia that have survived and successfully reproduced in Florida are occasionally decimated by a winter cold front.[10]

In January, 2011, a selective fish kill affecting an estimated 2 million juvenile spot fish was attributed to a combination of cold stress and overpopulation after a particularly large spawn.[11]

Spawning fatalities

Fish kill due to spawning fatalities can occur when fish are exhausted from spawning activities such as courtship, nest building, and the release of eggs or milt (sperm). Fish are generally weaker after spawning and are less resilient than usual to smaller changes in the environment.

Disease

Fish are subject to various viruses, bacteria and fungi in addition to parasites such as protozoans, flukes and worms, or crustaceans. These are naturally occurring in many bodies of water, and fish that are stressed for other reasons, such as spawning or suboptimal water quality, are more susceptible. Signs of disease include sores, missing scales or lack of slime, strange growths or visible parasites, and abnormal behavior – lazy, erratic, gasping at the water surface or floating head, tail or belly up.

For example, since 2004 fish kills have been observed in the Shenandoah River basin in the spring, from the time water temperatures are in the 50s (°F) until they reach the mid-70s. So far, investigators suspect certain bacteria, along with environmental and contaminant factors that may cause immune suppression.[12]

In fish farming, where populations are optimized for the available resources, parasites or disease can spread quickly. In channel catfish aquaculture ponds, for example, the “hamburger gill disease” is caused by a protozoan called Aurantiactinomyxon and can kill all the fish in an affected pond. In addition to altered behavior, affected fish have swollen gills that are mottled and have the appearance of ground hamburger meat. [13]

Some early warning signs of fish suffering from disease or parasite infections include:[14]

  1. Discoloration, open sores, reddening of the skin, bleeding, black or white spots on the skin
  2. Abnormal shape, swollen areas, abnormal lumps, or popeyes
  3. Abnormal distribution of the fish such as crowding at the surface, inlet, or pond edges (though crowding at the surface during specific times of day, such as early morning, is more likely a sign of low oxygen)
  4. Abnormal activity such as flashing, twisting, whirling, convulsions, loss of buoyancy
  5. Listlessness, weakness, sluggishness, lack of activity
  6. Loss of appetite or refusal to feed

Toxins

Agricultural runoff, sewage, surface runoff, chemical spills, hazardous waste spills can all potentially lead to water toxicity and fish kill. Some algae species also produce toxins. In Florida, these include Aphanizomenon, Anabaena and Microcystis. Some notable fish kills in Louisiana in the 1950s were due to a specific pesticide called endrin.[15]

Human-induced fish kills are unusual, but occasionally a spilled substance causes direct toxicity or a shift in water temperature or pH that can lead to fish kill. For example, in 1997 a phosphate plant in Mulberry, Florida, accidentally dumped 60 million gallons of acidic process water into Skinned Sapling Creek, reducing the pH from about 8 to less than 4 along for about 36 miles and resulting in the death of about 1.3 million fish. [16]

It is often difficult or impossible to determine whether a potential toxin is the direct cause of a fish kill. For example, hundreds of thousands of fish died after an accidental spill of bourbon into the Kentucky River near Lawrenceburg. However, officials could not determine whether the fish kill was due to the bourbon directly or to oxygen depletion that resulted when aquatic microbes rapidly began to consume and digest the liquor.[17]

Underwater explosions

Underwater explosions can lead to fish kill, and fish with swim bladders are more susceptible. Sometimes underwater explosions are used on purpose to induce fish kills, a generally illegal practice known as blast fishing. Underwater explosions may be accidental or planned, such as for construction, seismic testing, mining or blast testing of structures under water. In many places, an assessment of potential effects of underwater explosions on marine life must be completed and preventive measures taken before blasting.[18]

Estimation

Estimating the magnitude of a kill presents a number of problems.[19]

  1. Polluted waters are often very turbid or have low transparency making it difficult or impossible to see fish that have sunk
  2. Rivers and streams can move fish downstream out of the investigation area.
  3. Small fish and fry can decompose or become buried in sediments very quickly and are lost from the count.
  4. Predators and scavengers remove and eat fish.
  5. Stressed fish may swim up tributaries and die there
  6. Many kills are reported only when dead fish resurface due to decompositional gas formation, often several hours after the kill has occurred.

Some very large fish kills may never be estimated because of these factors. The discharge of red aluminium sludge from a reservoir in Hungary into the Marcai River is acknowledged as causing environmental devastation,[20] The loss of adult fish also can have long term impacts on the success of the fishery as the following year's spawning stock may have been lost and recovery of the pre-kill population may take years to recover. The loss of food supplies or recreational income may be very significant to the local economy.[21]

Investigation

Many countries in the developed world have specific provisions in place to encourage the public to report fish kills[22] so that a proper investigation can take place.[23] Investigation of the cause of a kill requires a multi-disciplinary approach including on-site environmental measurements, investigation of inputs, review of meteorology and past history, toxicology, fish autopsy, invertebrate analysis and a robust knowledge of the area and its problems.[24]

Notable events

The counts given below are all estimates. They tend to be underestimates, and may omit, for example, small fish, those removed by scavengers and those that settle to the bottom.[19]

Event/Location Date Count Species Remarks
Gulf of Mexico (Corpus Christi) 1935 22,000,000 Caused by red tide. Also caused coughing, sneezing and watery red eyes in humans.[25]
River Aeron 1974 10,000 salmon, trout Discharge of creamery waste through poorly maintained sewer. Successful prosecution followed.
River Neath 1976 50,000 salmon, trout Extreme drought left fish stranded in stagnant pools into which sewers drained.
River Ogmore 1979 50,000 salmon, trout Spillage of Kymene from a paper mill on the River Llynfi a tributary of the Ogmore. Successful prosecution followed and substantial compensation.
Gulf of Mexico 1986 22,000,000 Gulf menhaden, striped mullet, various other species[26] Caused by red tide.[25]
Rhine River 1986 01 500,000 Caused by spill from Swiss chemical warehouse[27]
Texas coast 1997–1998 21,000,000 Caused by a bloom of Karenia brevis[28][29]
River Dee (United Kingdom) 2002 07 100,000 [30] salmon, trout, roach, perch Unconfirmed link to release of whey into river
Neuse River, North Carolina 2004 09 1,900,000 menhaden "Natural upwelling" of an acknowledged polluted river. Hydrogen sulfide smell reported[31]
Liuxihe River Guangzhou People's Republic of China 2008 09 09 10,000 carp Unknown[32][33]
Beaches at Thanet, Kent, England 2010 01 20,000 velvet crab 20000 + dead crabs - along with dead starfish, lobsters, sponges and anemones. Probably killed by hypothermia.[34][35]
Ting River Fujian People's Republic of China 2010 07 >1,000,000 Enough to feed 70,000 people a year[36] Part of the Zijin mining disaster[37]
Mississippi River; Plaquemines Parish, Louisiana 2010 09 100,000[38] redfish, trout, flounder
Arkansas River; Ozark, Arkansas 2010 12 100,000[39] freshwater drum Coincided with death of 5,000 red-winged blackbirds that fell from the sky.
Chesapeake Bay 2011 01 2,000,000 spot croakers Included some juvenile croakers. Cold water stress was believed to be the cause.[40]
Jiaxing Xiuzhou District People's Republic of China 2011 01 06 250,000 catty Largest damage was 170,000 catty in zone A stall number 48. Only fish raised from a river under China National Highway 320 east is dead.[41][42]

See also

References

  1. ^ University of Florida. Gainesville, FL (2005). "Fish kill." Plant Management in Florida's Waters.
  2. ^ Noga, Fish Disease: Diagnosis and Treatment, 2010, John Wiley and Sons ISBN 0813806976, p. 316
  3. ^ A Beginner’s Guide to Water Management – Fish Kills, Information Circular 107, University of Florida IFAS Extension, 2003 read online
  4. ^ http://www.engineeringtoolbox.com/oxygen-solubility-water-d_841.html
  5. ^ Fish Kills in Coastal Georgia Ponds and Lagoons, Georgia Department of Natural Resources
  6. ^ Fish kill in Estonia lake in 2002 due to combination of algae bloom and high temps
  7. ^ Read the news story online at chicagobreakingnews.com
  8. ^ August 2010 fish kill in Delaware Bay linked to high temperatures – low oxygen
  9. ^ Reuter’s News Service report of massive fish kill at the mouth of the Mississippi River in September, 2010. The Division of Wildlife stated that the fish kill was unrelated to the oil spill that had recently occurred in the Gulf of Mexico. [http://www.aolnews.com/2010/09/16/massive-mississippi-river-fish-kill-not-bps-fault/ read related story online
  10. ^ A Beginner’s Guide to Water Management – Fish Kills, Information Circular 107, University of Florida IFAS Extension, 2003 read online
  11. ^ CNN story on Jan 6, 2011 Fish kill in Maryland
  12. ^ information from the Department of Environmental Quality, Virginia, USA; see also History of fish kills in the Shenandoah watershed, Virginia
  13. ^ A Beginner’s Guide to Water Management – Fish Kills, Information Circular 107, University of Florida IFAS Extension, 2003 read online
  14. ^ Fish Kills - Their Causes and Prevention, Virginia Tech, Virginia Cooperative Extension Publication 420-252, 2009
  15. ^ Larson et al., 1997, Pesticides in Surface Waters: distribution, trends and governing factors. CRC Press ISBN 1575040069 p. 278
  16. ^ A Beginner’s Guide to Water Management – Fish Kills, Information Circular 107, University of Florida IFAS Extension, 2003 read online
  17. ^ A Beginner’s Guide to Water Management – Fish Kills, Information Circular 107, University of Florida IFAS Extension, 2003 read online
  18. ^ Lewis, 1996, Effects of Underwater Explosions on Life in the Sea, report DSTO-GD-0080 to the Australian Department of Defence read online; Govoni, et al., 2008, Effects of Underwater Explosions on Larval Fish: Implications for a Coastal Engineering Project, Journal of Coastal Research 2(S):228-233 doi: 10.2112/05-0518.1
  19. ^ a b Labay, Andrew A.; Bizan, Dave (1999). "A Comparison of Fish Kill Counting Procedures on a Small, Narrow Stream". North American Journal of Fisheries Management. 19 (1). American Fisheries Society: 209–214. doi:10.1577/1548-8675(1999)019<0209:ACOFKC>2.0.CO;2.
  20. ^ "Hungarian chemical sludge spill reaches Danube". BBC News. 2010-10-07.
  21. ^ Environment Agency, UK (2009). "Life after a fish mortality."
  22. ^ Florida Fish and Wildlife Research Institute - Submit A Fish Kill Report
  23. ^ Environment Agency, UK (2010-12-22). "Fish mortality investigations."
  24. ^ Pierce, Robert A.; May, Thomas W.; Suppes, V. Charles (1994). "Collection and Submission of Samples for Fish-Kill Investigation and Toxic-Substance Analysis." University of Missouri Extension, Columbia, MO. Publication No. G9402.
  25. ^ a b Reisinger, E. Anthony (2000). "Red Tide." Coastal Studies Laboratory, University of Texas-Pan American. Edinburg, TX.
  26. ^ Trebatoski, Bob (1988). "Observations on the 1987-1987 Texas Red Tide (Ptychodiscus brevis)." Texas Water Commission, Austin TX. Report No. 88-02.
  27. ^ Environmental History Timeline
  28. ^ Science House (North Carolina State University). "Algae Blooms." Investigating the Ocean. Accessed 2011-01-07.
  29. ^ Bushaw-Newton, K.L. and Sellner, K.G.(1999). "Harmful Algal Blooms." NOAA's State of the Coast Report. Silver Spring, MD: National Oceanic and Atmospheric Administration.
  30. ^ BBC News | WALES | Pollution toll rises to 100,000 fish
  31. ^ Book, Sue (2009-09-04). "Neuse fish kill estimate now closer to 2 million". Sun Journal. New Bern, NC.
  32. ^ Chinadaily.com.cn. "Chinadaily.com.cn." Dead fish mystery in Guangzhou probed. Retrieved on 2010-01-08.
  33. ^ hk.apple.nextmedia.com. "hk.apple.nextmedia.com." 廣州流溪河污染　魚屍數萬條. Retrieved on 2010-01-08.
  34. ^ "Thousands of dead crabs wash up on Kent beaches". BBC News. January 13, 2010. Retrieved January 10, 2011.
  35. ^ Winter Crab deaths - the statistics and a ramble - Thanet coast life Retrieved on 2011-01-08
  36. ^ National geographics. "National Geographic." Water pollution disaster. Retrieved on 2010-01-08.
  37. ^ Bloomberg.com. "Bloomberg.com." Zijin mining officials fined 1.16 million yuan for waste spills in fujian. Retrieved on 2010-01-08.
  38. ^ "Massive La. Fishkill Prompts Oil Spill Questions Hundreds of Thousands of Dead Fish in Bayou Near Mississippi River; Oil, Chemical Dispersant, Oxygen Levels Eyed as Culprits". CBS News. September 15, 2010. Retrieved 2011-01-07. Plaquemines Parish officials spotted a massive fish kill on Friday. Hundreds of thousands of dead fish were floating west of the Mississippi River, in Bayou Chaland. It came several days after the discovery of starfish kill in nearby Barataria Bay. Then, on Monday, came the discovery of a dead baby whale near Venice. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
  39. ^ "Massive fish kill blankets Arkansas River". CNN. January 3, 2011. Retrieved 4 January 2011. Dead drum fish floated in the water and lined the banks of a 20-mile stretch of the Arkansas River near Ozark, about 125 miles northwest of Little Rock, said Keith Stephens of the Arkansas Game and Fish Commission. A tugboat operator discovered the fish kill Thursday night, and fisheries officials collected some of the dying animals to conduct tests. ...
  40. ^ Maryland Department of the Environment, Baltimore, MD (2011-01-05). "MDE Investigates Large Fish Kill in Chesapeake Bay." Press release.
  41. ^ News.big5.enorth.com.cn. "News.big5.enorth.com.cn." 嘉興一水產市場2.5萬斤魚暴斃 或有人投毒. Retrieved on 2010-01-08.
  42. ^ Tech-food.com. "Tech-food.com." 浙江嘉兴市水产批发市场约2.5万斤鱼死亡. Retrieved on 2010-01-08.
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